There is an increasing demand for alkylate fuel blending feedstock. As a fuel-blending component alkylate combines a low vapour pressure, no sulfur, olefins or aromatics with high octane properties. The most desirable components in the alkylate are trimethylpentanes (TMPs), which have research octane numbers (RONs) of greater than 100. Such an alkylate component may be produced by reacting isobutane with a butene or a mixture of butenes in the presence of a suitable acidic catalyst, e.g. HF or sulfuric acid, although other catalysts such a solid acid catalyst have been reported. Recently, the alkylation of isoparaffins with olefins using an acidic ionic liquid catalyst has been proposed as an alternative to HF and sulfuric acid catalysed alkylation processes.
For instance, U.S. Pat. No. 7,285,698 discloses a process for manufacturing an alkylate oil, which uses a composite ionic liquid catalyst to react isobutane with a butene. In the process of U.S. Pat. No. 7,285,698, isobutane and a butene are supplied to a reactor and the alkylate is formed by contacting the reactants with a composite ionic liquid under alkylation conditions. The reactor effluent is separated and the ionic liquid phase is recycled to the reactor while the hydrocarbon phase is treated to retrieve the alkylate. However, during operation of such an ionic liquid alkylation process solids are formed. As the reaction progresses, these solids accumulate in the reaction zone and may lead to blockage of pathways and/or valves. In WO2011/015639 a process is described for removal of the solids formed during the ionic liquid alkylation process. According to that process, a solids-comprising effluent comprising hydrocarbons and acidic ionic liquid is withdrawn from the reaction zone and at least part of the solids-comprising effluent is treated to remove at least part of the solids to obtain a solids-depleted effluent. It has however been found that solids removal according to the process of WO2011/015639 is difficult because of high viscosity of the ionic liquid. Centrifugation of the solids-comprising effluent is therefore complex and is accompanied by high energy consumption. Filtration is not very practical because it is time consuming and requires high pressures. Finally, settling is even more time consuming and therefore not a desirable solution.